Collecting biomaterial for laboratory research is a delicate, but a critical procedure, the accuracy of which often determines the correct diagnosis. Patients often wonder whether it is possible to take a test collected in the evening, and where it is best to keep it until it is delivered to the laboratory. Errors at the stage of sample preparation and storage can lead to false results, which will lead to unnecessary treatment or the omission of a serious disease.
Temperature conditions are a key factor in preserving the biological properties of the material. Pathogenic microorganisms helminth eggs react differently to cold, and improper handling of the container can destroy traces of their vital activity. In this article we will analyze all the nuances of the temperature regime so that you can be confident in the reliability of the medical reports obtained.
Many people mistakenly believe that the colder the better, and they send the jar to the freezer. This is a serious mistake that makes the biomaterial unsuitable for most types of research. The structure of the cells is destroyed during freezing, and enzymatic processes are stopped or distorted, which renders the analysis useless for the doctor.
The critical importance of the temperature regime during storage
The preservation of the viability of microorganisms and the structure of the biomaterial directly depends on the ambient temperature. Bacteriological culture requires special conditions, since many bacteria during sudden When cooled, they die or go into an inactive state that cannot be detected by standard methods. That is why the question of where to store feces - in the refrigerator or freezer - should not raise any doubts: only above-zero temperatures.
At room temperature, the processes of rotting and fermentation begin almost immediately after defecation. Actively reproducing microflora changes the chemical composition of the sample, which is especially critical for analyzes on occult blood or carbohydrates. The refrigeration chamber allows you to slow down these processes, but does not stop them completely, so the time window for donating material is limited.
Freezing the biomaterial leads to crystallization of moisture inside the cells. When ice turns to water, the cell walls burst and the contents mix, making microscopic examination impossible. Frozen stool is absolutely not suitable for any type of standard laboratory analysis.
It is important to understand that different departments of the laboratory require different approaches. If in bacteriology cold can kill a culture, then in coprology (the study of physical properties) it can change the consistency beyond recognition. Therefore, adherence to the regime +2...+4°C is the gold standard for short-term storage.
⚠️ Attention: Never place a container with biomaterial on the shelf of the refrigerator door. There, the temperature constantly fluctuates due to frequent opening, which can lead to sample damage. Use the middle shelves of the main compartment.
Why the freezer is completely excluded
Using a freezer to store biomaterial is a common misconception that is often found among patients who want to “save” the analysis longer. At temperatures below -18°C water, which makes up a significant part of feces, turns into ice. This process irreversibly changes the physicochemical properties of the sample.
For analysis on dysbacteriosis or intestinal group a living or at least structurally preserved flora is required. Freezing kills most anaerobic bacteria, which are key indicators of gut health. As a result, the laboratory will issue a conclusion about the absence of flora or sterility, which is a false diagnosis.
Even if we are talking about a simple test for worm eggs, freezing can destroy the shells of some types of parasites or change their optical properties, making identification under a microscope difficult. The laboratory technician simply will not be able to see what should be visible, or will mistake crystallization artifacts for pathological inclusions.
In addition, there is a risk of cross-contamination. Storing biological waste near food, even in closed containers, violates basic sanitary standards. Vapors and microparticles can settle on products, creating a risk of infectious contamination of household members.
What to do if the material accidentally freezes?
If you find that the container is frozen, do not try to defrost it and take it to the laboratory. This sample is no longer suitable. You will have to collect new material, since the results will be deliberately false and may mislead the doctor.
Rules for storage in the refrigerator for various tests
The refrigerator is the only acceptable place for temporary storage, but there are some nuances here too. The basic rule is: the less time passes between collection and research, the more accurate the result. However, life makes adjustments, and sometimes you have to store the material for several hours.
For analysis on occult blood (Gregersen's reaction) the requirements are especially strings. Blood in the stool quickly oxidizes and changes color, and hemoglobin is destroyed by enzymes. It is advisable to deliver such material within 2-3 hours, but storage in the refrigerator for up to 6-8 hours is allowed, provided it is sealed.
Research on worm eggs and protozoa are more resistant to external influences. Some types of cysts can maintain their shape for up to 24 hours in the cold. However, living forms of protozoa (for example, amoebas) lose mobility and shrink when cooled, which makes them difficult to detect, so to search for them, the material must be warm.
Bacteriological cultures (for dysbacteriosis, intestinal group) require maximum sterility and speed. Opportunistic pathogenic flora begins to multiply faster than beneficial flora, changing the balance. Staphylococcus aureus or Klebsiella can give a false positive result during long-term storage even in the cold.
Shelf life of biomaterial: correspondence table
Time is the enemy of the accuracy of laboratory research. Every hour spent outside the body changes the composition of the sample. Below is a table that will help you figure out how long the material can be stored under different conditions.
It is important to consider that the indicated periods are relevant only if the rules for collection in a sterile container are followed. If the material was collected in a non-sterile container or in contact with urine/water, its shelf life is reduced to zero.
| Type of analysis | At room temperature | In the refrigerator (+2...+4°C) | In the freezer |
|---|---|---|---|
| For worm eggs and protozoa | Up to 2-4 hours | Up to 24 hours (not recommended) | Unsuitable |
| For occult blood | Up to 2 hours | Up to 6-8 hours | Unsuitable |
| Bacterial culture (dysbacteriosis) | No more than 1 hour | Up to 2 hours (maximum) | Unsuitable |
| Coprogram (general) | Up to 4-5 hours | Up to 8-10 hours | Unsuitable |
As can be seen from the table, the range permissible temperatures are narrow. Room temperature permissible only as a last resort and for a very short time, as it accelerates all biochemical processes. The refrigerator acts as a buffer that slows down the decay, but does not stop it.
⚠️ Attention: If you store the material in the refrigerator for more than 6 hours, be sure to notify the laboratory assistant or doctor about this. This may affect the interpretation of results, especially in pH and the presence of leukocytes.
Technique for collecting and preparing containers
Correct collection is 50% of diagnostic success. The use of inappropriate containers (matchboxes, yogurt jars) is unacceptable. Residues of detergents, chemicals or microbes from the surface may react with the biomaterial.
For collection, you must use special sterile containers, which are sold in pharmacies. They are equipped with a spatula built into the lid, which allows you to take the material without touching the walls with your hands. This ensures sterility samples.
The collection process should take place in a dry, clean container (vessel, pot, film stretched over the toilet). Contact with toilet water or disinfectants that you used to wash the potty is not allowed. Chlorine or other reagents may kill bacteria or change the color of the sample.
The volume of material should be approximately the size of a walnut or 1-2 teaspoons. There is no need to fill the container to the brim, since when opening the lid in the laboratory, the contents may contaminate the hands of personnel or the outer part of the container.
☑️ Checklist before taking the test
Features of transportation to the laboratory
Even if you have correctly collected and stored the material, it still needs to be delivered to the laboratory. In summer or hot weather, the temperature in the bag can quickly rise, negating all efforts to store it in the refrigerator.
Use thermal bags or thermal containers with cold elements (cold accumulators) if travel time exceeds 30-40 minutes. This will maintain a stable temperature and prevent the sample from overheating. However, remember that direct contact of the container with ice is also undesirable.
During transportation, the container must be in an upright position, tightly closed. It is advisable to place it in an opaque bag to maintain ethical and hygienic aspects. Do not leave biomaterial in a car in direct sunlight or near operating heating devices.
If you are taking an analysis to a private laboratory, find out about the possibility of calling a courier. Professional couriers know how to transport biomaterials and have the necessary equipment to maintain the “cold chain” temperature regime.
Common mistakes and myths about storing tests
There are many myths that exist among patients. One of the most dangerous is the belief that adding preservatives or water will extend the life of the sample. This is absolutely forbidden to do unless the doctor or laboratory assistant gives specific instructions.
Another mistake is collecting material “with reserve”. Some patients collect the test 2-3 days in advance in order to accurately submit it. This is pointless, since during this time irreversible changes occur in the sample, and it becomes biological waste rather than diagnostic material.
The need for labeling is also often ignored. If you're donating multiple containers (for example, from different family members or different portions), be sure to label each one. Confused tests lead to erroneous treatment.
You shouldn’t rely on “maybe”. If you doubt whether you saved the material correctly, it is better to retake it. Treatment based on false data can cause real harm to health, especially when it comes to prescribing antibiotics.
⚠️ Attention: Test rules and laboratory requirements may vary slightly. Always check the leaflet issued by a particular medical institution, or check the requirements on their official website before your visit.
Is it possible to store stool in the refrigerator overnight before donation?
Yes, for most tests (for worm eggs, coprogram, occult blood), storing it in the refrigerator overnight (8-10 hours) is acceptable. However, for bacteriological culture (dysbacteriosis) this is already the deadline, and the result may be less accurate. Ideally, collect the material in the morning, 2-3 hours before delivery.
What to do if it is not possible to take the analysis right away?
If you cannot take the analysis right away, place a tightly closed container in the refrigerator on the middle shelf. Don't freeze it. Try to deliver the material to the laboratory as soon as possible, but no later than 24 hours from the moment of collection (for tests for parasites).
Does taking medication affect the result if the material was stored correctly?
Yes, taking antibiotics, bismuth, iron and some other medications can distort the result, even if the storage was ideal. Be sure to tell your doctor about all medications you are taking. It is usually recommended to take a pause after taking antibiotics before taking a microflora test.
Is it possible to take a test if urine has entered the container?
No, such a test cannot be taken. Urine contains bacteria and chemicals that change the pH and composition of stool. This will lead to false results. It is necessary to collect new material, excluding the ingress of urine.
Is it necessary to warm up the material before handing it over if it was in the refrigerator?
No, there is no need to specifically warm up the material. However, if you are transporting it during the cold season, make sure that it does not freeze along the way. In the laboratory, samples will still be brought to room temperature before testing, but it is better to exclude sudden changes.